Typically Class D architectures employ multiple feedback loops in order to attain all performance goals in the system. Primarily power supply rejection ratio (PSRR) and distortion are the most difficult issues to surmount. Since an ideal Class D amp has zero output impedance and switches the load terminal between ground and the power supply, it has no power supply rejection. Class D outputs are also susceptible to errors introduced by non-ideal, non-symmetric H-bridge switching.